Phase shifter for pulse producers



April 5, 1949, E. H. SCHOENFELD PHASE SHFTER FOR PULSE PRODUCERS 5 Sheets-Sheet vl Filed March 28, 1946 www l l. l law. mmbwl i IJ -MIIII NVENTOR.

l w MMU@ April 5, 1949. E. H. SCHOENFELD PHASE SHIFTER FOR PULSE PRODUCERS 3 Sheets-Sheet 2 Filed March 28, 1946 5A TURA 7/ April 5, 1949. E. H. SCHQENFELD PHASE SHIFTER FOR PULSE PRODUCERS 5 Sheets-Sheet 3 Filed March 28, 1946 fum; rE

ATTIPZVEX Patented Apr. 5, 1949 PHASE SHIFTER FOR PULSE PRODUCERS Earl Schoenfeld, Mamaroneck, N. Y., assignor. to Radio Corporation of America, a corporation.

of Delaware Application March 28, 1946, Serial No. 657,686

1 Claim.

My invention relates to phase shifting apparatus and particularly to a method of and means for. shifting. the timingv or. phase of electrical pulses.

The present invention is particularly applicable to radio navigation Asystems of the type known as Loran systems. Such a system is described in application Serial No, 5606l8, filed October 27, 1944, in the name of George D. Hulst, Jr., Patent No. 2,430,570, lNovember 11,: 1947., and entitled Radio navigationsystem. .Y It is the preferred practice to `utilize inrthese systems a chain of frequencydividersof theftype that Hprovides a pulse output. It may be desirable to shift the phase of a pulse from theV divider chainin a continuous and; uniform manner. throughv more than 360vdegrees .so that, after Aa pair-of received pulses have been aligned :by such` a phase shift, the reading-.in microseconds Yrequired for Loran navigation canbe read directly off the phase shifter scale.

Such. a continuousand uniform phase shift of a pulse is obtained in thenavigation systems lmown-asShoranl systems by utilizing goniometer type -phaseshifter :units -which are geared together, thisl being feasible because .the Shoran systems employ a chainV of frequencyl divider units that have sine wave outputs. Thus, the sine wave. outputs may` bevisupplied .to the goniometer unitswhich, yof course, require a sine wave source. inthe. Loranv systems, since the frequency dividerchain supplies pulsesv4 instead of f sinev waves.: a plurality of geared goniometer units cannot'beused unlessr the pulses are first converted. to `sinevwaves. Such conversion results in undesirable.complication 'of thev system.

An object of thelpresent invention is to provide an-.improvedmethodr-of and means for shifting the :phase of electrical pulses..

A further object of the. ,invention is to provide animproved method ofandmeans for shifting the phase cfa pulse continuously through more than.360 degrees.

According to a preferred.l embodiment of the invention, the pulse vfromeach unit `of a frequency divider. chainis delayed a variable amount by supplying it to a sawtooth generatonto produce av sawtooth wave.v The sawtooth wave is passed through. a clippingcircuit. that hasy its slipping level determined by...a variable ,bias so that the L front edgeg-ofa pulse `produced bythe clipping circuiti-starts at;a time determined bythe bias setting. A The. pulse-thus lproducedfis differentiated whereby -there is obtained thedesireddelayed ,pulse kwhich hasthesame timingas said (Cl. Z-36) front edge. The variable bias controls of the several delay circuits are geared together with the gear ratio for each bias control the same as the amount of frequency division at the corresponding frequency divider unit.

The delayed pulses thus obtained from the several clipper circuits are applied to a pulse selector, described hereinafter, so that there is obtained a pulse that may be shifted in phase through many times 360 degrees. The use of a pulse selector in this way is describedV for use with a Shoran system in application Serial No. 638,387, filed December 29, 1945, in the name of Stuart W. Seeley and entitled Radio navigation system.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which:

Figure 1 is a block and circuit .diagram of one embodiment of the invention,

Figure 2 is a group of graphs that are referred to in explaining-the operation of the apparatus shown in Fig. 1,

Figures 3, 4 and 5 are circuit diagrams of bias varying circuits -that may be employed in the apparatus of Fig. 1,

Figure 6 is a group of graphs that are referred to in explaining the operation of the pulse selector included in the circuit of Figl l, andl Figure 7 is a circuit diagram of a pulse selector.

In the several gures, similarparts are indicated by similar reference characters.

Fig. 1 shows a crystal oscillator I0 and a frequency divider chaincomprising two frequency divider units II and I2, each of which divides by five in the example illustrated, The oscillator Ill khas a sine wave output indicated by the graph I3 whilel the dividers II and I2 have pulse outputs such as the blocking oscillator outputs indicated by the graphs I4 and I6.

The divider chain output pulses I6 are supplied to a sawtooth wave generator I'I which, as shown in Fig. 2, producessawtooth voltage waves I8 in synchronism with the applied pulses. The sawtooth waves I3 are supplied over a coupling capacitor 2I to the grid of a clipping tube 22.

Variable negative bias is supplied to the grid ofthe tube 22 by means of a biasing circuit which comprises a battery 23 across which is connected a potentiometer resistor 24 having a variable tap 26. thereon carried by a rotatable arm 21. The potentiometer arm 21 is connected through a resistor 28 to the gridof the tube 22. A fixed negative bias may be supplied in addition to the variable bias by a battery 29.

The output of the clipping tube 22 is a rectangular pulse 3|. The timing of the front edge of the pulse 3| is determined, as shown in Fig. 2, by the level at which the sawtooth wave I 8 is clipped, and this in turn is determined by the position of the potentiometer arm 21. As shown in Fig. 1, the position of arm 21 may be changed by means of a hand wheel 32 coupled to the arm 21 through a train of gears whereby the front edge of the pulse 3| is shifted.

The pulse 3| is differentiated by a dierentiating circuit comprising a capacitor 33 and a resistor 34 to obtain the ware form 36 shown in Fig. 2. The wave 36 is then passed through a clipping diode 31 to obtain the positive pulses 36a only, and these are supplied over a conductor 38 to a pulse selector 39.

The output pulses I4 of the frequency divider are supplied over a conductor to a delay circuit that is similar to the delay circuit just described and in which similar parts are indicated by the same reference number with a prime added. The pulses indicated at 52 are supplied over a conductor 53 to the pulse selector 39. The pulses 52 have a repetition rate that is five times that of the pulses 36a. Also, the pulses 52 are narrower in width than the pulses 36a.

The potentiometer arm 21 is rotated by means of the hand wheel 32 at five times the rate of rotation of the potentiometer arm 21 since the drive for the arm 21 is through gears 58 and 59 having a 1 to 1 ratio Whereas the drive for the arm 21 is through gears 56 and 51 having a 1 to 5 ratio.

The sine wave output I3 of the oscillator l0 is supplied over a conductor 6| to a goniometer type phase shifter 6.2. The output of the phase shifter 62 may be supplied to a pulse shaper 63 which clips or otherwise shapes the sine Wave to produce a periodic pulse 64 which is supplied to the pulse selector 39. If preferred, the pulse shaper 63 may be omitted and a half cycle portion of the sine wave signal utilized as the pulse 64. The pulse 64 is narrower than the pulse 52 and has a periodic rate that is the same as the frequency of the oscillator I8.

The rotor of the phase shifter 62 is rotated at five times the rate'of the potentiometer arm 21' since it is driven directly by the hand wheel 32 while the arm 21 is driven through a pair of gears 66 and 61 which have a 1 to 5 ratio and through the gears 58 and 59 having a 1 to 1 ratio.

Fig. 7 shows one example of a pulse selector. It comprises a vacuum tube 1| having a plurality of grids which are so biased that no signal appears in the plate circuit unless the pulses 64, 52, and 36a are on the grids simultaneously. Any suitable biasing, such as grid leak biasing, may be employed.

Fig. 6 shows how the phase shift of the pulse 36a selects first one of the pulses 52 and then another, and how the selected pulse 5.2 selects first one of the pulses 64 and then another. Thus a pulse 64, in effect, may be shifted continuously and uniformly through many times 360 degrees.

Figs. 3 and 4 show biasing potentiometer arrangements for avoiding an open circuit at the time the contact point 26 moves from one end of resistor 24 back to the starting end. In Fig. 3 this is accomplished by connecting the potentiometer arm 21 through a resistor 12 to the starting end of the potentiometer resistor 24. In

Fig. 4, it is assumed that the ends of the resistor 24 are so close together that they are both in contact with the contact point or slider element 26 as it moves into position to repeat a biasing cycle. Shorting of the battery 23 at this time is prevented by a resistor 13.

It will be evident that in operation the cutoff bias line (Fig. 2) jumps from the bottom end of the sawtooth wave to the top end of the sawtooth wave When the contact point or slider 26 completes a traversal of the potentiometer resistor 24 and moves again into contact with the starting end of the resistor 24. Further rotation then causes linear shift downward of the cutoff bias line. Thus there is obtained a continuous phase shift.

From the foregoing description it is apparent that the two potentials at the ends of the potentiometer resistor 24 should be equal to the maximum and minimum potentials, respectively, of the sawtooth wave applied to the grid of the clipping tube. A circuit for providing and maintaining this equality regardless of minor ampli tude variations in the sawtooth wave is shown in Fig. 5.

Referring to Fig. 5, the sawtooth wave from the generator |1 is applied over a conductor 16 and through coupling capacitors 11 and 18 to rectifier tubes 19 and 8|, respectively. Thus, the positive and negative half cycles of the saw-- tooth wave (with respect to its A-C. axis) are rectified by the tubes 19- and 8|. The rectified currents are smoothed or filtered by the capacitors 11 and 18 and by the leak resistors 82 and 83, respectively, so that they may be applied to the grids of a pair of amplifier tubes 84 and 86 for amplitude control of the bias voltage.

'I'he bias voltage is taken off the cathode resistors 81 and 88 of the tubes 84 and 86, respectively, and is supplied to the ends of the potentiometer resistor y24 through switches 89 and 9|. The tube 22 is cathode biased by an amount equal to its cut-off bias plus one-half the voltage across the potentiometer resistor 24. It will be apparent that a change in the amplitude of the sawtooth Wave will cause a corresponding change in the value of the bias voltage across resistor 24 as desired.

The cathode resistors 81 and 88 are each provided with tWo taps connected to switch contact points 92 and 94 and to contact points 93 and 96. The adjustment is such that with the switch arms 89 and 9| on the contact points 92 and 93, the potentials applied to the ends of resistor 24 equal the maximum and minimum potentials, respectively, of the sawtooth Wave.

The two taps for the contact points 94 and 96, however, are located so that the range of the bias voltage selected by the phase shifter is slightly less than the peak-to-peak voltage of the sawtooth Wave. Thus, there is avoided two momentary conditions when there would be no output pulse from the phase shifter. One of these conditions is when the potentiometer slider is set so that cut-off bias occurs at the very bottom of the sawtooth wave; then the conduction of the clipping tube is continuous. The other of these conditions is when the slider is set so that cut-off bias is at the very top of the sawtooth wave; then the clipping tube is non-conducting at all times.

With the switches 89 and 9| on the contact points 94 and 96, the phase shifter will have a small discontinuity as the slider crosses the break in the potentiometer resistor. However, by careful design this sudden phase jump can be kept small so that any effect on the output pulse selector can be avoided. It will be evident from an inspection of Fig. 6 that slight variations or jumps in the phase of the comparatively wide pulse 36a Will have no effect on the selection of a pulse 52 which is comparatively narrow. Likewise, slight jumps in the phase shift of a pulse 52 will have no effect on the selection of a pulse 64.

I claim as my invention:

In combination, means for producing pulses recurring at a periodic rate, means for producing a saWtooth Wave in response to the occurrence of each of said pulses, means comprising a clipping tube,I and variable biasing means for said tube for clipping said sawtooth waves at a certain clipping level to produce pulses each having an edge that occurs at a time depending upon said clipping level, said variable bias means including means for rectifying and filtering a portion of said saWtooth Wave signal whereby said bias changes in amplitude in response to a change in the amplitude of said sawtooth Wave,

6 means for diiferentiating said last pulses to produce delayed pulses each occurring at the same ti-me as said edge whereby the timing of said delayed pulses may be varied by Varying said clipping level, means for Varying said bias for varying said clipping level, and means for passing only said delayed pulse to a utilization circuit.

EARL I-I. SCHOENFELD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,105,870 Vance Jan. 18, 1938 2,171,536 Bingley Sept. 5, 1939 2,277,000 Bingley Mar. 17, 1942 2,355,363 Christaldi Aug. 8, 1944 FOREIGN PATENTS Number Country Date 510,881 Great Britain Aug. 8, 1939 

